It is well known to have a built-in heating element for providing heat to the body of the occupant of the driver seat and/or the passenger seat of a motor vehicle. The heat is provided by electric current supplied through a conductor having suitable resistivity that ensures the desired amount of heat from the conductor. The conductor, in the form of a resistance wire, is located on a layer of textile or a plastic material to provide a carrier in the form of a planar or flat sheet. The resistance wire is fixed in position on the carrier by stitching means or by an adhesive and, afterwards, positioned between various layers of material to form the heating element which then can be incorporated into a seat. In this regard, the heating element can be sandwiched between a top cover member of leather, fabric or plastic material and the foam rubber core portion or padding of the seat.
Seats provided for vehicles used for material handling, earthmoving, or lawn cutting are normally fabricated utilizing an in-mold forming process to reduce the cost of the seat. This type of process provides a seat having a core made of a plastic foam, such as polyurethane foam, that is bonded to an outer decorative cover sheet or skin during the molding process. In the practice of such process, a properly shaped mold cavity is lined with a thin plastic or fabric skin after which liquid polyurethane is poured onto the skin to form an integral seat cushion or seat back. Various attempts have been made to provide a relatively inexpensive seat of this type that would have a heating element incorporated between the skin of the article and the foam layer. In most cases, such attempts have resulted in the configuration of the heating element and/or the conductor being outlined in the cover sheet and, therefore, not acceptable from an aesthetic standpoint. Obviously, if the heating element could be spaced from the skin a certain distance, maintained in such position, and completely encapsulated in the foam during the molding operation, the “reading” of or outline of the heating element would not be visible to the observer.
There has also been the problem in providing a comfortable “feel” to the buttocks of a seat occupant when seated in a seat assembly having a heating element as a part of the seat structure. Inasmuch as the heating element needs to be positioned relatively close to the outer skin of a seat member and becomes an integral part of the foam structure, it stands to reason that the heating element should be designed and constructed so that it does not take away from the softness and comfort of the seat. In other words, not only should the heating element within the seat not be detectable from an appearance standpoint but, in addition, the heating element should not cause the seat to provide any substantially less comfort when occupied than would be attainable if the heating element was not a part of the seat.